Digital subscriber line induction neutralizing transformer network

ABSTRACT

A digital subscriber line (DSL) induction-neutralizing transformer (INT) ( 28 ) for use in a DSL INT network ( 10 ) is provided. The DSL INT ( 28 ) includes a core ( 72 ) and a coil ( 74 ) that is electrically coupled to and wound around the core ( 72 ). The coil ( 74 ) includes approximately 100-200 feet of approximately 24-gauge wire. The core ( 72 ) and coil ( 74 ) add longitudinal inductance to a telecommunication line and reduce induced voltage levels at a non-digital subscriber line frequency on the telecommunication line. The DSL INT network ( 10 ), containing at least one DSL INT ( 28 ), and a method of routing DSL communication signals within the DSL INT network ( 10 ), are also provided.

TECHNICAL FIELD

[0001] The present invention relates generally to data transmissionsystems, and more particularly, to an apparatus and method of routingdigital subscriber line communication signals within a digitalsubscriber line induction neutralizing transformer network.

BACKGROUND OF THE INVENTION

[0002] Demand for high-speed data transmission is ever increasing.Internet access, electronic commerce, Internet protocol telephony, andvideoconferencing are telecommunications examples driving such a demand.

[0003] Digital subscriber line (DSL) technology provides high-speed datatransmission over a so-called “last mile” of “local loop” of a telephonenetwork via copper twisted wire pair cable between residential and smallbusiness sites and telephone company central offices and remoteterminals. There are various types of DSL such as asymmetric DSL, highbit-rate DSL, single-line DSL, very-high-data-rate DSL, integratedservices digital network DSL, and rate-adaptive DSL having varioustransmission rates, switched circuit characteristics, and other knownoperation characteristics. These are collectively referred to as XDSLtechnologies.

[0004] In a simplified general view, a DSL system may be considered as apair of communicating modems, one of which is located at a home oroffice computer, and the other of which is located at a network controlsite, typically at a telephone company central office or a remoteterminal. The central office or remote terminal modem is connected tosome type of network, usually referred to as a backbone network, whichis in communication with other communication paths by way of routers ordigital subscriber line access multiplexers (DSLAMs). Through DSLAMs thebackbone network is able to communicate with dedicated informationsources and with the Internet. As a result, information accessible tothe backbone network may be communicated between the central office orremote terminal modem and a customer site modem.

[0005] DSL applications may be served from central office and remoteterminal locations by up to 12,000 feet of copper twisted wire paircable that may exist between the DSLAM equipment at a central office orremote terminal and a DSL modem at a customer site. However, cable froma remote terminal is typically exposed to a more hostile electricalenvironment that can cause service reliability problems. These problemsbecome highly prevalent in areas of high earth resisitivity, which isusually in soil equal to or greater than 500 meter ohms.

[0006] Additionally, although most telecommunication networks have aprimary-line protector that is allocated for each customer site as wellas for the central offices and remote terminals, the primary-lineprotector does not protect against induced voltages that are less than300 volts. Steady-state induced voltages of 20-30 volts can causesignaling and equipment malfunctions to the DSLAM equipment and to theDSL modem as well as reducing advertised transmission line speeds. Worseyet, surge-induced voltages and resulting induced currents exist on theabove mentioned wire-line style cable applications when carrying acommunication signal between various locations, and may also exist underthe operation of the primary-line protector. The surge-induced voltagescan cause damage to sensitive electronic components in the DSLAMequipment, such as a line card and the DSL modem equipment, renderingthe service inoperable. Also, impulse noise spikes can occur that canreduce the effective speed of the data transmission.

[0007] Historically, AC induction problems have come from the long loopsserving customers at the ends of an exchange area boundary, which arethe most distant customer terminal locations within local calling areasfrom a central office. These loops are not only predominantly exposed tounbalanced, single phase power lines, but the areas they serve are insuburban/rural environments that are less “built-up”, and additionalshielding benefits are not available as in urban areas.

[0008] Neutralizing transformers were originally designed for use inopen wire telephony networks. Large oil-filled neutralizing transformershave been used on wire-line facilities entering power substations and ingenerating plants to suppress high-induced alternating current (AC)voltages and ground potential rise (GPR). Smaller dry-type neutralizingtransformers, known as induction neutralizing transformers (INTs), havebeen used to reduce voice-frequency noise and induced AC voltages from350-600 volts on wire-line voice-grade and digital carriertelecommunications circuits.

[0009] However, the voice-grade INTs are typically made with up to 500feet of 26 gauge Category 3 cable, which not only reduces the availabletransmission overhead margins which limits their application on DSLapplications, but also increases the probability of crosstalk couplinginterference on adjacent DSL circuits. As the length of a copper pair isextended, the signal power decreases in intensity, thereby, limiting theallowable distance between a customer terminal and a central office orremote terminal. Also, the higher the frequency application, as withDSL, the more noticeable the diminution in signal power. The use of avoice-grade INT reduces signal power approximately 2.3 dB at lower DSLfrequencies.

[0010] Digital-grade INTs are typically wound with up to 200 feet of 24gauge Category 3 cable, and are built with a screen (shield) to separatetwo directions of T1 carrier transmissions, to prevent crosstalkinterference. Digital grade INTs exhibit a lower signal power loss overvoice-grade INTs, but as with voice-grade INTs they are large, heavy,and expensive units because of the 350-600 volt design criteria. Thecosts involved in manufacturing and implementing both digital-grade INTsand voice-grade INTs is high. The screen is a significant added cost andis not required in DSL applications.

[0011] An additional impairment with high-speed DSL transmission speedsis crosstalk interference between adjacent circuits. The crosstalk canbe minimized by using non-adjacent pairs within a binder group. However,the non-adjacent pairs become tightly wound together for several hundredfeet in an INT. Coil-winding of the INT tends to spread the Category 3cable wire pairs out and thus increases the probability of crosstalkinterference between the closely coupled pairs.

[0012] It would therefore be desirable to develop a high-speed digitaltelecommunication network containing voltage neutralizing devices thatreduce lower level steady-state and surge induced voltages and that aresuitable for DSL applications, including being smaller in size, lighterin weight, and less expensive to manufacture and implement as comparedto traditional INTs. In so doing, a more reliable telecommunicationnetwork is created to satisfy the ever-increasing demand for high-speedcommunication at customer terminals that are at great distances from acentral office.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a block diagrammatic view of a digital subscriber line(DSL) induction neutralizing transformer (INT) network in accordancewith an embodiment of the present invention;

[0014]FIG. 2 is a schematic diagram of a DSL circuit in accordance withan embodiment of the present invention;

[0015]FIG. 3 is a pictorial view of a DSL INT in accordance with anembodiment of the present invention; and

[0016]FIG. 4, is a logic flow diagram illustrating a method of routingDSL communication signals within the DSL INT network.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0017] In each of the following figures, the same reference numerals areused to refer to the same components. While the present invention isdescribed with respect to a digital subscriber line (DSL) inductionneutralizing transformer (INT) and a DSL INT network including the DSLINT therein for use in a telecommunication system, the present inventionmay be adapted to be used in various communication systems including:telecommunication systems, DSL systems, high-speed data transmissionsystems, or other communication systems.

[0018] In the following description, various operating parameters andcomponents are described for one constructed embodiment. These specificparameters and components are included as examples and are not meant tobe limiting.

[0019] Also, in the following description the terms “telecommunicationline” refer to any telecommunication signal path medium.Telecommunication line may refer to various telecommunication cablessuch as fiber optic cable or copper twisted wire pair cable.Telecommunication line may also refer to telecommunication deviceslocated along a telecommunication signal path including central offices,remote terminals, DSL circuits, customer terminals, and othertelecommunication devices.

[0020] The present invention provides a digital subscriber line (DSL)induction neutralizing transformer (INT) for use in a telecommunicationsystem. The DSL INT includes a core and a coil that is electricallycoupled to and wound around the core. The coil includes approximately100-200 feet of approximately 24-gauge wire. The core and coil addlongitudinal inductance to a telecommunication line and reduce inducedvoltage levels at a non-digital subscriber line frequency on thetelecommunication line.

[0021] A DSL INT network and a method for providing the same are alsoprovided including one or more remote terminals routing DSLcommunication signals to a plurality of customer terminals. The INTnetwork also includes one or more DSL circuits. At least one DSL circuitreceives an excitation current from the induced voltage levels andincludes one or more transformer exciting networks (TENs) that supplyone or more low impedance paths-to-ground for the excitation current. Adigital subscriber line induction neutralizing transformer iselectrically coupled to the one or more transformer exciting networksand neutralizes the induced voltage levels in response to the excitationcurrent.

[0022] One of several advantages of the present invention is that itprovides an induced voltage neutralizing device that is much smaller insize, lighter in weight, and less expensive to manufacture and implementas compared to traditional INTs.

[0023] Another advantage of the present invention is that it provides ahardened network that is capable of providing more reliable high-speedDSL transmissions to customers served at the ends of an exchange areaboundary over wire-line facilities.

[0024] Furthermore, the present invention provides a high-speed DSL INTnetwork with minimal signal power loss, and eliminates the potential forcrosstalk interference. The present invention also provides an apparatusfor better neutralizing induced voltages at the power influence harmonicfrequencies that can help reduce the effects of impulse noise.

[0025] Referring now to FIG. 1, a block diagrammatic view of a DSL INTnetwork 10 in accordance with an embodiment of the present invention, isshown. The DSL INT network 10 includes a backbone network 12 andmultiple customer terminals 14. The DSL INT network 10 routes DSLcommunication signals between the backbone network 12 and the customerterminals 14. The backbone network 12 is electrically coupled tomultiple central offices 16 which, in turn, are electrically coupled tomultiple remote terminals 18 via fiber optic cables 20. The fiber opticcables 20 allow the remote terminals 18 to be at relatively largedistances from the central offices 16 without noise, alternating current(AC) induction, or impedance problems associated with traditional coppertwisted wire cables. The remote terminals 18 are electrically coupled tomultiple DSL circuits 22, which are electrically coupled to the customerterminals 14. The customer terminals 14 may communicate with the DSL INTnetwork 10 via DSL modems, not shown.

[0026] The remote terminals 18 are generally located in a moresuburban/rural environment as opposed to the central offices 16, whichare located in a more urban environment. The remote terminals 18 incombination with the DSL circuits 22 provide high-speed datatransmission to customer terminals 14 at the ends of an exchange areaboundary. The remote terminals 18 contain DSL access multiplexer (DSLAM)equipment to provide the DSL service.

[0027] The DSL circuits 22 include one or more transformer excitingnetworks (TENs) 24, preferably two TENs per DSL circuit to protectequipment both at the remote terminals 18 and at the customer terminals14, as shown with TEN_(A1a1) and TEN_(A1a2) for a first circuit 26, witha DSL INT 28 therebetween. Although a pair of TENs 30, including firstTENs 31 and second TENs 32, are illustrated for each DSL circuit 22,various combinations of TENs 24 may be used, depending upon theapplication. For example, a pair of TENs 24 may be located on one DSLcircuit of concern, associated with a specified DSL INT 28, whereasother DSL circuits associated with the specified DSL INT 28 need notcontain any TENs 24. This is illustrated by first circuit 26 andcustomer terminals A1 a and A1 b. The DSL circuit of concern thatcontains the pair of TENs 30 does not need to be a working circuit or acircuit in servicing operation, but it must have end-to-end continuityfrom the remote terminal 18 to the far end 37 and to customer terminal14.

[0028] The present invention includes several different DSL INT 28 sizesfor the different sized cables that are electrically coupling thevarious telecommunication devices. For example, cables 33 extending awayfrom the remote terminals 18, towards the customer terminals 14, areknown as F1 “feeder cables”. The feeder cables are then divided anddownsized to smaller F2 “distribution” cables 35 within serving areainterface (SAI) cross-connect boxes 34 between the remote terminals 18and the customer terminals 14. Since the remote terminals 18 are servingsmaller subscriber distribution areas in rural environments, the cables33 may only have 25, 50, or 100 twisted wire pairs per cable as opposedto 300 or more twisted wire pairs as in larger distribution areas. Whenlarger F1 cables are used, multiple DSL INTs 28 are utilized in paralleloperation for full count treatment. Note, in order to minimizeinterference and maximize performance, all twisted wire pairs within aF1 cable are preferably neutralized in order to achieve the bestresults, especially at power influence and harmonic frequencies and withimpulse noise.

[0029] In certain applications an additional DSL INT 28 may need to beadded between the SAI 34 and a customer terminal 14, as illustrated byDSL INT_(B2a2). For example, the F2 distribution cables 35 are onlycross-connected to the F1 feeder cables 33 when a customer subscribes toa DSL service, therefore there may be a small amount of working circuitswithin the F2 cable 35. Thus, in order to achieve maximum effectiveness,particularly at higher interfering frequencies and with impulse noise,the additional DSL INT may need to be installed so that all twisted wirepairs within the cable 35 become neutralized. When the additional DSLINT is used an additional TEN, such as TEN_(B2a2), is preferably usedbetween the SAI 34 and the DSL INT_(B2a2).

[0030] In one embodiment of the present invention the first TEN 31 isinstalled between the remote terminals 18 and the DSL INT 28. The secondTEN 32 is installed at a far end 37 of the cable 35 that is beingtreated. For multiple paralleling DSL INTs 28 for cables larger than 100pairs, a pair of TENs 30 is similarly installed to provide theexcitation current for each DSL INT 28 for the remaining DSL circuits22.

[0031] The TENs 24 prevent the need for grounding and wasting avaluable, revenue-producing copper pair within a telecommunication cableroute in order to make the DSL INT 28 function properly. The TENs 24provide low impedance paths-to-ground for the necessary excitationcurrent flow through the DSL INT 28. The excitation current is generatedby an induced voltage from a paralleling power line to thetelecommunication cable. The induced voltage may be on thetelecommunications line continuously, due to a steady-state source, ormay be surge induced, such as by lightning or a momentary power-linefault. All telecommunication lines within a cable sheath 36 must passthrough one or more DSL INTs 28, such as DSL INT_(A1a).

[0032] The DSL INTs 28 are preferably located near the remote terminals18, so as to remove a maximum amount of induced voltage and current fromacting on any remote terminal DSLAM equipment or customer terminal DSLmodems. The DSL INTs 28 generate a counter electromagnetic field or“bucking” voltage, which is 180° out of phase from the induced voltage,and neutralizes or cancels out the undesired induced voltage.

[0033] In another embodiment of the present invention all twisted wirepairs 39 associated with a specific remote terminal 18 extend through aDSL INT 28, whether all corresponding DSL circuits 22 have DSL serviceor not. This provides additional “full-count” protection for DSLAM linecards that may be within the remote terminals 18. Maximum neutralizationeffectiveness is achieved when all twisted wire pairs 39 within atelecommunication cable sheath extend through a DSL INT 28, especiallywhen a DSL circuit is experiencing significant noise frequencies orimpulse noise spikes.

[0034] Additional protection devices, such as primary-line protectors orother protection devices known in the art, may be incorporatedthroughout the INT network 10. For example, the additional protectiondevices may be electrically coupled, non-intrusively of a DSLcommunication signal path, between the DSL INTs 28 and the second TENs32. However, protection devices are preferably not located at the DSLINTs 28, to prevent electrical shorting out the DSL INTs 28. When aprotection device is operated at a DSL INT 28, the protection devicecircuit location is reverted to ground potential, thereby performing asa TEN. Reverting the protection device circuit location to groundprevents the DSL INT 28 of interest from performing, since there is noexcitation current flow through the DSL INT 28.

[0035] Referring now to FIG. 2, a schematic diagram of the DSL circuits22 in accordance with an embodiment of the present invention, is shown.

[0036] The TENs 24 may be standard TENs as illustrated by a second TENcircuit 40, representing the second TEN 32, or may be Super TENs asillustrated by a first TEN circuit 42, representing the first TEN 31. ASuper TEN is similar to a standard TEN, but includes a harmonic drainagereactor 44. The harmonic drainage reactor 44 drains noise frequencyharmonic voltages to ground. The Super TENs act as a broadly tunedfilter for removing induced voltages at 50 Hz or 60 Hz frequencies,depending upon the particular country's power line operating frequency,and also the higher voice-frequency (power influence) harmonics. TheSuper TENs are preferred due to their better filtering performanceeffectiveness over standard TENs.

[0037] The first TEN 31 includes a first pair of capacitors 46 and afirst inductor 48 therebetween. The first pair of capacitors 46 areelectrically coupled respectively to a first “tip” wire conductor 50 anda first “ring” wire conductor 52 on a telecommunication line 54. Acenter-tapped terminal 56 of the first inductor 48 is electricallycoupled to a second inductor 58, which is then electrically coupled toground 60. The harmonic drainage reactor 44 includes a second pair ofcapacitors 62 electrically coupled to a third inductor 64 therebetween,which has a center-tapped terminal 65 electrically coupled to ground 60.The second pair of capacitors 62 are also electrically coupledrespectively to the first tip wire conductor 50 and the first ring wireconductor 52.

[0038] The DSL INT circuits 22 are designed to substantially reduce andmitigate the non-digital subscriber line frequencies of 50 Hz or 60 Hz,including the harmonic voice frequency interference and impulse noiselevels that may fall within the DSL frequency spectrum and causeinterference. The DSL INT 28 is represented by a DSL INT circuit 66. Thesecond TEN 32 is illustrated, as stated above, as a standard TEN and issimilar to a Super TEN except it does not have the harmonic drainagereactor 44.

[0039] Referring now to FIG. 3, a pictorial view of a DSL INT 28 inaccordance with an embodiment of the present invention, is shown. TheDSL INT 28 includes a permeable ferromagnetic core 72 and a coil 74wound around the core 72. The core 72 may be formed from a ferromagneticiron, nickel, or other similar electromagnetic material known in theart. The coil 74 is wound around the core 72 and includes approximately100-200 feet of category 5 type 24-gauge wire. Depending on the twistedwire pair size of the DSL INT, the core 72 and coil 74 can addapproximately 6 to 25 Henries of longitudinal inductance to a typicaltelecommunication line. Although the coil 74 is formed from category 5Ethernet-type local area network (LAN) telecommunication cable, whichcontains tightly twisted wire pairs, other similar cable, known in theart, may be used. The coil 74 has several physical characteristics, someof which include being color-coated, unjacketed, and unshielded. Thetightly twisted wire pairs mitigate cross coupling of adjacenthigh-frequency signals onto surrounding circuits, thus minimizing anycrosstalk interference problems.

[0040] When the core 72 and coil 74 are excited, via the proper amountof excitation current, the induced voltage levels are reduced at the endof the telecommunication line. The core 72 and the coil 74 willinstantaneously neutralize and collect at least 95% of approximately50-100 volts that have been induced on a telecommunication line, whetherthe induced voltage is on the line continuously or is on the line for ashort duration.

[0041] Besides acting as induced voltage neutralizing devices, the DSLINTs 28, also act as induced current limiting devices. In so doing, theDSL INTs 28 reduce increased induced current magnitudes in atelecommunication line due to the use of the fiber optic cable 20 ratherthan traditional copper twisted wire pair cable between the centraloffices 16 and the remote terminals 18. Moreover, the DSL INTs 28 addhigh longitudinal impedance to the DSL circuits 22, which effectivelyreduces the harmonic induced current flow which can cause noiseinterference.

[0042] Although not necessary, the DSL INT 28 can be designed to bepackaged in the form of a direct-burial unit for a number ofconstruction, aesthetic, safety and maintenance reasons, which are knownin the art.

[0043] Referring now to FIG. 4, a logic flow diagram illustrating amethod of routing DSL communication signals within the INT network 10,is shown.

[0044] In step 100, the central offices 16 route the DSL communicationsignals between the backbone network 12 and the remote terminals 18.

[0045] In step 102, the remote terminals 18 route the DSL communicationsignals between the central offices 16 and the DSL circuits 22.

[0046] In step 104,at least one DSL circuit receives an excitationcurrent having a non-digital subscriber line frequency. The non-digitalsubscriber line frequency may be a frequency equal to 50 Hz or 60 Hz, asstated above.

[0047] In step 106, the first TENs 31 supply the first low impedancepaths-to-ground, thereby allowing the necessary induced current to flowthrough the DSL INT 28.

[0048] In step 108, the second TENs 32 supply second low impedancepaths-to-ground at the far ends 37 of the cable route being treated.

[0049] In step 110, the DSL INTs 28 add from 6 to 25 Henries oflongitudinal inductance to a telecommunication line in response to theexcitation current to suppress induced harmonic currents that can causenoise interference. When exciting currents are high enough, the DSL INT28 neutralizes 60 Hz induced voltages as follows: 5 ma @ 20 volts, 10 ma@ 40 volts and 20 ma @ 100 volts, for example.

[0050] In step 112, the customer terminals 14 receive and transmit theDSL communication signals to and from the DSL circuits 22.

[0051] The above-described steps are meant to be an illustrativeexample, the steps may be performed synchronously or in a differentorder depending upon the application.

[0052] The present invention increases operational reliability anddecreases the amount of malfunctions of remote terminal DSLAM equipmentand customer DSL modems and protects these devices from being damaged byinterfering power sources and lightning surges. Additionally, there is asignificant reduction in induced power influence or harmonic voltagesand currents and impulse noise that can cause circuit interruptions andslower data transmission rates. Resulting signal-to-noise ratioimprovements allow for longer DSL circuit applications, in turnresulting in greater numbers of customer terminals that may be serviced.

[0053] The above-described apparatus, to one skilled in the art, iscapable of being adapted for various purposes and is not limited to thefollowing systems: automotive vehicle systems, control systems,communication systems, or other communication systems. Theabove-described invention may also be varied without deviating from thespirit and scope of the invention as contemplated by the followingclaims.

What is claimed is:
 1. A digital subscriber line induction neutralizingtransformer for use in a digital subscriber line induction neutralizingtransformer network comprising: a core; and a coil electrically coupledto and wound around said core and comprising approximately 100-200 feetof approximately 24 gauge wire; said core and said coil addinglongitudinal inductance to a telecommunication line and reducing inducedvoltage levels at a non-digital subscriber line frequency on saidtelecommunication line.
 2. A transformer as in claim 1 wherein addinglongitudinal inductance comprises adding approximately 6 to 25 Henriesof inductance to said telecommunication line.
 3. A transformer as inclaim 1 wherein said induced voltage levels are generated from asteady-state source or are surge-induced.
 4. A transformer as in claim 1wherein said core is a permeable ferromagnetic core formed from aferromagnetic iron or nickel material.
 5. A transformer as in claim 1wherein said core and said coil neutralize at least 95% of approximately50-100 volts on said telecommunication line instantaneously whether saidinduced voltage levels are generated from a steady-state source or aresurge-induced.
 6. A transformer as in claim 1 wherein said coilcomprises category 5 Ethernet type telecommunication cable comprisingtightly twisted wire pairs.
 7. A transformer as in claim 1 wherein saidcoil is at least one of: color-coated, unjacketed, plastic-insulated, orunshielded telecommunication cable.
 8. A transformer as in claim 1wherein said non-digital subscriber line frequency is approximatelyequal to 50 Hz or 60 Hz.
 9. A digital subscriber line inductionneutralizing transformer network comprising: one or more remoteterminals routing digital subscriber line communication signals to aplurality of customer terminals; and one or more digital subscriber linecircuits wherein at least one digital subscriber line circuit receivesan excitation current from an induced voltage, said one or more digitalsubscriber line circuits comprising; one or more transformer excitingnetworks electrically coupled to a remote terminal of said one or moreremote terminals and supplying one or more low impedance paths to groundfor said excitation current; and a digital subscriber line inductionneutralizing transformer electrically coupled to said one or moretransformer exciting networks and neutralizing induced voltage levels inresponse to said excitation current.
 10. A network as in claim 9 furthercomprising one or more central offices electrically coupled to said oneor more remote terminals via one or more fiber optic cables and routingsaid digital subscriber line communication signals between said one ormore remote terminals and a backbone network.
 11. A network as in claim9 wherein at least one transformer exciting network in the digitalsubscriber line induction neutralizing transformer network is a supertransformer exciting network comprising a harmonic drainage reactor. 12.A network as in claim 9 wherein supplying one or more low impedancepaths to ground said one or more transformer exciting networks reduceapproximately 50 Hz or 60 Hz induced voltage levels and current levels.13. A network as in claim 9 wherein a first transformer exciting networkof said one or more transformer exciting networks is electricallycoupled between a remote terminal and said digital subscriber lineinduction neutralizing transformer.
 14. A network as in claim 9 whereina second transformer exciting network of said one or more transformerexciting networks is electrically coupled at a customer terminal site.15. A network as in claim 9 wherein said digital subscriber lineinduction neutralizing transformer comprises: a core; and a coilelectrically coupled to and wound around said core and comprisingapproximately 100-200 feet of approximately 24 gauge wire; said core andsaid coil adding longitudinal inductance to a telecommunication line andreducing induced voltage levels at a non-digital subscriber linefrequency on said telecommunication line.
 16. A transformer as in claim15 wherein said coil comprises category 5 Ethernet typetelecommunication cable comprising tightly twisted wire pairs.
 17. Anetwork as in claim 9 further comprises one or more additionalprotection devices.
 18. A network as in claim 17 wherein said one ormore additional protection devices are electrically couplednon-intrusively of a digital subscriber line communication signal pathbetween said digital subscriber line induction neutralizing transformerand said second transformer exciting network.
 19. A method of routingdigital subscriber line communication signals within a digitalsubscriber line induction neutralizing transformer network, said methodcomprising: routing digital subscriber line communication signalsbetween a backbone network and one or more remote terminals; routingsaid digital subscriber line communication signals between one or morecentral offices and one or more digital subscriber line circuits;receiving an induced voltage level and an excitation current; supplyinga first low impedance path-to-ground for said excitation current;supplying a second low impedance path-to-ground for said excitationcurrent; neutralizing said induced voltage level in response to saidexcitation current; and routing said digital subscriber communicationsignals to one or more customer terminals.
 20. A method as in claim 19wherein neutralizing said non-digital subscriber line frequencycomprises adding approximately 6 to 25 Henries of inductance to saidtelecommunication line.